The results of five years of field corrosion testing of three-layer copper-nickel-chromium coatings with an external layer of microporous chromium, unchromated and electrochemically chromated, have been described and discussed. The corrosion testing was carried out in four natural atmospheres: industrial, urban, marine, and rural. A marked positive influence of chromating on corrosion resistance and durability of tested coatings has been found. Thicker Cu20 Ni20b Cr mp, both chromated and unchromated, coatings with external layer of microporous chromium can be used in all natural atmospheres in which the testing was carried out for at least six years without any corrosion changes.